Phosphate rocks contain calcium phosphate minerals largely in the form of apatite, usually together with other minerals, e.g. silicate minerals and carbonate minerals, such as calcite. Apatite is a generic name for a group of calcium phosphate minerals also containing other elements or radicals, such as fluorapatite, chlorapatite, hydroxylapatite, carbonate-rich fluorapatite and carbonate-rich hydroxylapatite.
Phosphate ore froth flotation is a conventional process for recovering apatite from ore pulps. Most widely used anionic flotation agents for flotation of phosphate ores are the unsaturated fatty acids, for example oleic acid, and the technical grades or commercial grades of naturally-occurring fatty acid mixtures having a high proportion of unsaturated fatty acids, such as tall oil, acids from soybean oil, cottonseed oil and linseed oil, and derivatives thereof, as well as synthetic acids. The unsaturated fatty acid flotation agents are known to be comparatively non-selective because they are also suitable for the flotation of carbonate containing minerals, and therefore have only limited use in cases where accompanying minerals such as these have to be separated off from the valuable apatite minerals. There are a lot of suitable anionic surfactants proposed to be used as flotation agents for calcium phosphate, such as, for example, alkyl benzene sulfonates, alkyl phosphates, alkyl sulfates, alkyl sulfosuccinamates, alkyl sulfosuccinates, alkyl lactylates and alkyl hydroxamates. It is also known that these types of surfactants usually cannot be used in a pure form since they do not provide right froth characteristics during the flotation process, and therefore anionic surfactants are usually used in formulations together with other anionic (especially of fatty acid type) or nonionic surfactants.
However there is a need for new formulations of collectors for complex, for example weathered, ores, which are selective, based on renewable raw materials and easily manufactured.
WO 93/06935 discloses a method for producing iron-ore concentrates by the flotation washing (reverse flotation) of iron ore using as the collector mixtures containing at least one ether amine, and at least one other anionic and/or nonionic collector, which may be e.g. an acyl lactylate or a sarcoside. WO 92/21443 discloses a collector mixture for the flotation of non-sulfidic ores, which contains salts of sulfonation products of unsaturated fatty acids and salts of sulfonation products of unsaturated fatty acid glycerine esters, plus, optionally other anionic and/or nonionic surface-active agents, which may be acyl lactylates or sarcosides. WO 91/18674 discloses dicarboxylic acid esters with fatty acid monoalkanolamides as collectors for the flotation of non-pyritiferous ores, in particular apatite, and these collectors may also be mixed with acyl lactylates or sarcosides, and WO 91/15298 discloses the same collector for the flotation of non-sulfidic ores. U.S. Pat. No. 4,457,850 discloses acyl lactylates as flotation aids for the flotation of non-sulfidic minerals, WO 98/08597 discloses an emulsifier blend containing an acyl lactylate as the primary emulsifier and a nonionic surfactant as the coemulsifier, and U.S. Pat. No. 2,744,825 discloses the preparation of acyl lactylates. U.S. Pat. No. 4,732,667 discloses a process for froth flotation of iron ores, containing silicate and phosphate minerals that are floated away from the iron, using a collector mixture of a primary amine and e.g. a sarcoside. EP 0 201 815 B1 discloses the use of mixtures of at least one EO/PO adduct of a fatty alcohol and at least one anionic, cationic or ampholytic surfactant, that may be e.g. an acyl lactylate or a sarcoside, as collectors in the flotation of non-sulfidic ores.
However, there is still a need for more efficient collectors to be used in the froth flotation of phosphate ores to recover apatite.